In an attempt to translate the progress we have made in understanding the basic biology of immune reconstitution, we are engaged in clinical trials of tumor immunization and immune reconstitution for patients with high risk pediatric sarcomas. Initially, two trials were open (97-C-0050 and 97-C-0052). In both trials, tumor specific immunization is undertaken by the use of peptide pulsed dendritic cells. The peptide which is used is derived from the breakpoint region of the tumor specific translocations found in Ewing's sarcoma [t(11;22)] and alveolar rhabdomyosarcoma [t(2;13)]. In the first series of patients, 16 patients receive autologous elutriated monocytes which were pulsed with the peptides and high does IV interleukin-2 on 97-C-0050. We observed one mixed clinical response and one biologic response in this group. We also identified significant problems with T cell depletion in heavily pretreated patients as well as very large tumor burdens using standard Phase I entry criteria. The results of this trial were published: A Pilot Trial of Tumor-Specific Peptide Vaccination and Continuous Infusion Interleukin - 2 in Patients with Recurrent Ewing's Sarcoma and Alveolar Rhabdomyosarcoma: an Inter-Institute NIH Study R Dagher, LM Long , EJ Read, SF Leitman, CS Carter, M Tsokos, TJ Goletz, N Avila, JA Berzofsky , LJ Helman, CL Mackall, Medical and Pediatric Oncology, 2002. In summary, we concluded that while the responses seen were of interest, and the toxicity of this approach was minimal, future trials should focus on recruiting patients with smaller tumor burdens and more optimal immunity so that the potential benefits of immunotherapy may be better tested. We thus began to focus our efforts on patients with minimal residual disease first enrolling a total of 9 patients on a second clinical trial (97-C-0052) which utilized the same peptide pulsed vaccine as well as autologous T cell transfusion as a means for immune reconstitution. Importantly these patients are at high risk for disease recurrence, but are not required to have evaluable disease at the time of immunotherapy. Endpoints are evidence for immune reconstitution and measurable immune responses to the vaccine. We noted one patient with a transient biologic response to the vaccine and one patient with a positive immune reconstitution response. Several of the nine patients were not evaluable for immune reconstitution due to young age or insufficient T cell depletion at the time of enrollment. Of these nine patients, six remain alive and three remain free of disease, but whether the immune based therapies contributed in any way to this outcome remains unclear. In the next cohort, we sought to optimize the dendritic cells used for immunization in hopes of improving the rate of measurable biologic responses. We thus developed an M-CRADA with Immunex Corp. to obtain CD40 ligand for further maturation of the dendritic cells. Treatment of this cohort using CD40 ligand matured DCs began enrollment in January 2001. Nine patients have completed therapy with T cell infusions and CD40 ligand matured DCs. Six patients are alive and 4 of these are free of disease. With regard to biologic endpoints, we continue to see disappointing biologic responses to the peptide pulsed vaccine. While one potential explanation for this is potentially inadequate HLA binding of the translocation derived peptides, it is important to note that we also have not induced responses to an irrelevant HPV derived peptide which shows avid binding to HLA-A2. Thus, we are concerned that the low biologic response rate could relate to impairments in immune reconstitution. With regard to immune reconstitution endpoints, we observe some increase in total CD4 counts compared to historical controls, but there is a dramatic increase in the portion of the CD4 compartment which is comprised of CD25 cells. This appears to be related to the IL2 therapy administered since this is not observed in hosts undergoing immune reconstitution without IL2 therapy. Current studies are underway to determine whether the CD4+CD25+ cells generated in this study function as suppressor cells. A final cohort of patients is planned for 97-C-0052 which will utilize the same peptide pulsed dendritic cell vaccine but will delete IL2 and instead utilize the HIV protease inhibitor indinavir. Preclinical studies in our laboratory have shown indinavir to be immunorestorative in mice without retroviral infection and studies by other groups have shown that indinavir is capable of diminishing programmed cell death in human T cells. In summary, although we have not reproducibly generated tumor specific immunity in these patients which we can measure, these protocols have continued to accrue steadily reflecting an interest within the pediatric oncology community in developing immune based therapies for these diseases. The protocols have allowed us to generate standardized approaches for dendritic cell vaccines (Wong ECC, Maher VE, Hines K, Lee J, Carter CS, Goletz T, Kopp W, Mackall CL, Berzofsky JA and Read EJ. Generation of dendritic cells from peripheral blood monocytes for use in cancer immunotherapy. Cytotherapy 2001;3:19-30) and have provided important biologic information regarding the development of immunorestorative therapies. Finally, we have harvested T cells from patients enrolled on these trials which have provided important insights into the basic biology of the host tumor interface for patients with Ewings sarcoma (see project 4). Our plans are to continue to undertake immune based clinical trials for these diseases with an evolution toward alternative antigenic targets if insufficient biologic responses are observed in the next cohort of patients. AIDS RELATED 50%